Inertial driving actuator

ABSTRACT

An inertial driving actuator includes a fixing member, a moving element that is fixed to the fixing member and generates a small displacement by extension and contraction, an oscillation substrate that is fixed to the moving element and is moved linearly reciprocally by the small displacement, and a moving body that is moved by reciprocal movement of the oscillation substrate. The moving body has a first electrode. The oscillation substrate has a second electrode, the area of the facing portion of the second electrode and the first electrode changing continuously as the moving body moves. The actuator further includes a frictional force controller that controls a frictional force generated between the oscillation substrate and moving body, and a position detector that detects the position of the moving body on the basis of the electrostatic capacitance of the facing portion of the first electrode and the second electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2006-305725, filed Nov. 10, 2006,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an inertial driving actuator.

2. Description of the Related Art

Assume that a driving pulse with a waveform having a moderate rise and asubsequent sharp decay is applied to a piezoelectric element as a kindof electromechanical converting element. The piezoelectric elementmoderately extends at the moderate rise of the driving pulse, andquickly contracts at its sharp decay. An inertial driving actuator thatutilizes these characteristics is known. In the inertial drivingactuator, a driving pulse having the above waveform is applied to apiezoelectric element to generate oscillations having different speedsin the extending and contracting directions. This reciprocally moves adriving member fixed to the piezoelectric element at different speeds.Thus, a moving member frictionally coupled to the driving member movesin a predetermined direction.

Jpn. Pat. Appln. KOKAI Publication No. 2003-185406 discloses an inertialdriving actuator with a position detection function for a moving member.FIG. 10 shows this inertial driving actuator. In this inertial drivingactuator 100, one end of a piezoelectric element 120 is fixed to a frame110 of the actuator by means such as adhesion. A driving shaft 130 isfixed to the other end of the piezoelectric element 120 by means such asadhesion. A moving member 140 is frictionally coupled to the drivingshaft 130. A detection member 150 constitutes a fixed electrode todetect the position of the moving member 140 on the basis of anelectrostatic capacitance. The detection member 150 extends in parallelto the moving direction of the moving member 140 to be in non-contactwith the moving member 140, and is fixed to the frame 110. The drivingshaft 130, moving member 140, and detection member 150 are made of aconductive material. The detection member 150 has, on its surface thatfaces the moving member 140, uneven portions at a predetermined intervalin the moving direction of the moving member 140, thus forming anelectrode 151. The electrode 151 and moving member 140 face each otherat a gap D to form a capacitor.

When assembling the above inertial driving actuator 100, the drivingshaft 130 and detection member 150 must be maintained at a gap and aparallel degree respectively falling within allowable ranges. This isbecause in position detection utilizing an electrostatic capacitance, achange in gap between electrodes that form a capacitor may decrease thedetection accuracy.

BRIEF SUMMARY OF THE INVENTION

An inertial driving actuator according to the present invention includesa fixing member, a moving element that is fixed to the fixing member andgenerates a small displacement by extension and contraction, anoscillation substrate that is fixed to the moving element and is movedlinearly reciprocally by the small displacement, a moving body arrangedon the oscillation substrate, a first electrode formed on a surface ofthe moving body that faces the oscillation substrate, a second electrodeformed on a surface of the oscillation substrate that faces the movingbody, and an insulating film present between the first electrode and thesecond electrode. The moving body is moved by inertia with respect tothe oscillation substrate upon reciprocal movement of the oscillationsubstrate. As the moving body moves, the area of a facing portion of thefirst electrode and the second electrode changes continuously. Theinertial driving actuator further includes a frictional force controllerthat applies a voltage between the first electrode and the secondelectrode to exert an electrostatic force between them to control africtional force generated between the oscillation substrate and themoving body, and a position detector that detects a position of themoving body with respect to the oscillation substrate on the basis ofthe electrostatic capacitance of the facing portion of the firstelectrode and the second electrode.

Advantages of the invention will be set forth in the description whichfollows, and in part will be obvious from the description, or may belearned by practice of the invention. Advantages of the invention may berealized and obtained by means of the instrumentalities and combinationsparticularly pointed out hereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention, andtogether with the general description given above and the detaileddescription of the embodiments given below, serve to explain theprinciples of the invention.

FIG. 1 shows the arrangement of an inertial driving actuator accordingto the first embodiment of the present invention;

FIG. 2 is a timing chart of driving and position detection in theinertial driving actuator in FIG. 1;

FIG. 3 shows the arrangement of an inertial driving actuator accordingto the second embodiment of the present invention;

FIG. 4 is a timing chart of driving and detection in the inertialdriving actuator in FIG. 3;

FIG. 5 shows a circuit that detects the electrostatic capacitance in aposition detection circuit;

FIG. 6 shows the arrangement of an inertial driving actuator accordingto the first modification of the second embodiment;

FIG. 7 is a timing chart of driving and position detection in aninertial driving actuator according to the second modification of thesecond embodiment;

FIG. 8 shows the arrangement of an inertial driving actuator accordingto the third modification of the second embodiment;

FIG. 9 shows the arrangement of an inertial driving actuator accordingto the fourth modification of the second embodiment; and

FIG. 10 shows the arrangement of an inertial driving actuator having aconventional position detecting function.

DETAILED DESCRIPTION OF THE INVENTION

The embodiments of the present invention will be described withreference to the accompanying drawing.

First Embodiment

FIG. 1 shows the arrangement of an inertial driving actuator accordingto the first embodiment of the present invention.

As shown in FIG. 1, the inertial driving actuator comprises a fixingmember 10, a piezoelectric element 20 that generates a smalldisplacement by extension and contraction, an oscillation substrate 30that is moved nearly reciprocally by the small displacement, a movingbody 40 arranged on the oscillation substrate 30, and a piezoelectricelement driver 60 that drives to extend and contract the piezoelectricelement 20.

One end of the piezoelectric element 20 is fixed to the fixing member10, and the other end is fixed to one end of the oscillation substrate30. A spring is arranged between the other end of the oscillationsubstrate 30 and the fixing member 10. As the piezoelectric element 20extends or contracts, the oscillation substrate 30 reciprocally moves inthe extending/contracting direction with respect to the fixing member10.

The moving body 40 has a first electrode 41 on its surface that facesthe oscillation substrate 30. The oscillation substrate 30 has a secondelectrode 31 on its surface that faces the moving body 40. Theoscillation substrate 30 also has an insulating film 35 that covers thesecond electrode 31. The insulating film 35 is present between the firstelectrode 41 and the second electrode 31. The second electrode 31 has arectangular shape, and extends from the left end to the center of theoscillation substrate 30 along the straight line parallel to the movingdirection of the moving body 40 with respect to the oscillationsubstrate 30. The first electrode 41 and second electrode 31 always facepartially each other through the insulating film 35. As the moving body40 moves with respect to the oscillation substrate 30, the area of thefacing portion of the first electrode 41 and second electrode 31 changescontinuously. Namely, the area of the facing portion increases ordecreases depending on the moving direction of the moving body 40. Asthe moving body 40 moves, the facing portion of the first electrode 41and second electrode 31 changes in a dimension along the straight lineparallel to the moving direction of the moving body 40.

A permanent magnet 50 is arranged on the lower surface of the fixingmember 10, i.e., on a side opposite to the side where the oscillationsubstrate 30 is arranged. The permanent magnet 50 extends along astraight line parallel to the reciprocal direction of the oscillationsubstrate 30. The moving body 40 is made of a magnetic material. Hence,a magnetic attracting force acts between the moving body 40 andpermanent magnet 50 to hold the moving body 40 stably. A guide (notshown) supports the moving body 40 not to deviate from the movingdirection and not to separate from the oscillation substrate 30.

The inertial driving actuator also comprises a frictional forcecontroller 70 that applies a voltage between the first electrode 41 andsecond electrode 31 to exert an electrostatic force between them so asto control a frictional force generated between the oscillationsubstrate 30 and moving body 40, and a position detector 80 that detectsthe position of the moving body 40 with respect to the oscillationsubstrate 30 on the basis of the electrostatic capacitance of acapacitor formed by the facing portion of the first electrode 41 andsecond electrode 31. The position detector 80 comprises a positiondetection circuit 81 and a signal generation circuit 82. The positiondetection circuit 81 outputs a signal reflecting the electrostaticcapacitance of the facing portion of the first electrode 41 and secondelectrode 31. The signal generation circuit 82 applies a voltage such asa sine-waveform voltage to the first electrode 41 for position detectionof the moving body 40.

Driving and position detection in the inertial driving actuator of thisembodiment will be explained with reference to FIG. 2. FIG. 2 is atiming chart in the operation of moving the moving body 40 to the left.The position of the moving body 40 is detected after moving the movingbody 40. Namely, the step of moving the moving body 40 and the step ofdetecting the position of the moving body 40 are performed separately.

In the step of moving the moving body 40, the piezoelectric elementdriver 60 applies a trapezoidal-waveform voltage to the piezoelectricelement 20. The frictional force controller 70 applies arectangular-waveform voltage to the first electrode 41 and a constantvoltage to the second electrode 31. Upon application of thetrapezoidal-waveform voltage, the piezoelectric element 20 extends atthe rise of the trapezoidal waveform and contracts at its decay. Whenthe piezoelectric element 20 extends and contracts, the oscillationsubstrate 30 reciprocally moves on the fixing member 10. Therectangular-waveform voltage applied to the first electrode 41 has aperiod corresponding to the trapezoidal-waveform voltage applied to thepiezoelectric element 20, and takes a negative polarity at the rise ofthe trapezoidal waveform and a positive polarity at its decay. Thevoltage applied to the second electrode 31 has a positive polarity. Inone step of moving the moving body 40, a 1-pulse trapezoidal-waveformvoltage is applied to the piezoelectric element 20, and a 1-pulserectangular-waveform voltage is applied to the first electrode 41. Thevoltage applied to the piezoelectric element 20 is not limited to atrapezoidal-waveform voltage, but may be a triangular- orrectangular-waveform voltage.

In the section from A to B, the waveform applied to the piezoelectricelement 20 rises sharply. Thus, the piezoelectric element 20 extendsquickly, and accordingly the oscillation substrate 30 quickly moves tothe left. At this time, the voltage applied to the first electrode 41and that applied to the second electrode 31 have opposite polarities.Hence, an electrostatic chucking force acts between the oscillationsubstrate 30 and moving body 40, so that the frictional force generatedbetween them is comparatively large. Consequently, as the oscillationsubstrate 30 is displaced, the moving body 40 also moves to the left.

In the section from C to D, the waveform applied to the piezoelectricelement 20 falls sharply. Thus, the piezoelectric element 20 contractsquickly, and accordingly the oscillation substrate 30 quickly moves tothe right. At this time, the voltage applied to the first electrode 41and that applied to the second electrode 31 have the same polarity.Hence, no electrostatic chucking force acts between the oscillationsubstrate 30 and moving body 40, so that the frictional force generatedbetween them is comparatively small. Consequently, the inertia of themoving body 40 excels the frictional force between the oscillationsubstrate 30 and moving body 40, and the moving body 40 stays inposition.

As the result of these series of operations, the moving body 40 moves tothe left with respect to the oscillation substrate 30. The movingdistance at this time serves as the unit of movement of the moving body40. The step of moving the moving body 40 is thus ended.

In this embodiment, the operation of moving the moving body 40 to theleft has been described. To move the moving body 40 to the right, thepolarity of the waveform applied to the first electrode 41 may bereversed in the series of operations described above.

In the step of detecting the position of the moving body 40, voltageapplication of the piezoelectric element driver 60 to the piezoelectricelement 20 and that of the frictional force controller 70 to the firstelectrode 41 and second electrode 31 are stopped. The signal generationcircuit 82 applies a voltage, e.g., a sine-waveform voltage, to thefirst electrode 41.

Position detection of the moving body 40 is performed by detecting theelectrostatic capacitance of the facing portion of the first electrode41 and second electrode 31. The electrostatic capacitance of the facingportion of the first electrode 41 and second electrode 31 isproportional to the area of the facing portion, and the area changescontinuously depending on the position of the moving body 40. Thus, theposition of the moving body 40 is obtained by detecting the 5electrostatic capacitance of the facing portion of the first electrode41 and second electrode 31.

The position detection circuit 81 generates a signal reflecting theelectrostatic capacitance of the facing portion of the first electrode41 and second electrode 31 from a waveform that is output from thesecond electrode 31 upon application of the driving signal to the firstelectrode 41. The electrostatic capacitance is obtained from the peakvalue of the waveform output from the second electrode 31. Namely, theposition detection circuit 81 outputs the peak value of the waveformoutput from the second electrode 31. Consequently, the position of themoving body 40 is detected. The step of detecting the position of themoving body 40 is thus ended and, where necessary, the sequence returnsto the step of moving the moving body 40.

In position detection utilizing electrostatic capacitance, a change ingap between electrodes that form a capacitor decreases detectionaccuracy. In the inertial driving actuator of this embodiment, however,the moving body 40 is arranged in contact with the oscillation substrate30, and the first electrode 41 faces the second electrode 31 through theinsulating film 35. The thickness of the insulating film 35 determinesthe gap between the first electrode 41 and second electrode 31. Theinsulating film 35 preferably has a uniform thickness of several μm tosub μm. Such an insulating film 35 can be easily formed by asemiconductor process. Hence, the first electrode 41 and secondelectrode 31 are stably maintained at a narrow gap of several μm to subμm. Thus, the electrostatic capacitance of the facing portion of thefirst electrode 41 and second electrode 31 is detected with a highresolution, and the position of the moving body 40 is detected with ahigh accuracy. Namely, the inertial driving actuator of this embodimentis easy to assemble and high in position detection accuracy.

In the inertial driving actuator of this embodiment, the piezoelectricelement 20 is extended and contracted at the same speed. As the speed ofdisplacement of the piezoelectric element 20 does not change betweenextending displacement and contracting displacement, the drivingwaveform is simple.

According to this embodiment, the step of moving the moving body 40 andthe step of detecting the position of the moving body 40 are performedseparately at different times. This ensures driving and positiondetection. As the rectangular-waveform voltage is applied to the firstelectrode 41, when the piezoelectric element 20 extends, a stableelectrostatic chucking force acts between the oscillation substrate 30and moving body 40. This decreases variations in moving amount of themoving body 40, and the moving body 40 is moved with a stable unit ofpredetermined distance.

In the above description, the step of moving the moving body 40 and thestep of detecting the position of the moving body 40 alternate. However,the present invention is not limited to this. The step of moving themoving body 40 may be repeated a number of times, and after that thestep of detecting the position of the moving body 40 may be performed.

Second Embodiment

FIG. 3 shows the arrangement of an inertial driving actuator accordingto the second embodiment of the present invention. In FIG. 3, themembers denoted by the same reference numerals as in FIG. 1 are similarmembers. FIG. 4 is a timing chart of driving and detection in theinertial driving actuator of this embodiment.

According to this embodiment, an oscillation substrate 30 has anothersecond electrode 32 in addition to a second electrode 31. The secondelectrode 32 has the same shape as that of the second electrode 31 andis located on the same plane as the second electrode 31. The secondelectrodes 31 and 32 are arranged adjacent to each other along astraight line parallel to the moving direction of a moving body 40. Thesecond electrode 31 extends from the left end to the center of theoscillation substrate 30 and the second electrode 32 extends from theright end to the center of the oscillation substrate 30, along thestraight line parallel to the moving direction of the moving body 40. Afirst electrode 41 always partially faces both the second electrodes 31and 32 through an insulating film 35. As the moving body 40 moves, thearea of the facing portion of the first electrode 41 and secondelectrode 31 and that of the facing portion of the first electrode 41and second electrode 32 change continuously. Furthermore, of the areasof the two facing portions, one decreases and the other increasesdepending on the moving direction of the moving body 40. Morespecifically, with respect to the leftward movement of the moving body40, the area of the facing portion of the first electrode 41 and secondelectrode 31 increases, and that of the facing portion of the firstelectrode 41 and second electrode 32 decreases on the contrary. As themoving body 40 moves, the facing portion of the first electrode 41 andsecond electrode 31 and that of the first electrode 41 and secondelectrode 32 change in dimension along the straight line parallel to themoving direction of the moving body 40.

A position detection circuit 81 outputs a signal reflecting thedifference between the electrostatic capacitance of the facing portionof the first electrode 41 and second electrode 31 and that of the facingportion of the first electrode 41 and second electrode 32.

The driving scheme of the inertial driving actuator according to thisembodiment is substantially the same as that of the first embodiment.Note that in this embodiment, the same voltage as that applied to thesecond electrode 31 is applied to the second voltage 32.

As shown in FIG. 4, as the moving body 40 moves to the left, theelectrostatic capacitance of the facing portion of the first electrode41 and second electrode 31 increases gradually, and accordingly theoutput from the second electrode 31 also increases gradually. On thecontrary, the electrostatic capacitance of the facing portion of thefirst electrode 41 and second electrode 32 decreases gradually, andaccordingly the output from the second electrode 32 also decreasesgradually.

The position detection circuit 81 outputs a difference between the peakvalue of the output from the second electrode 31 and that of the outputfrom the second electrode 32. This difference in peak value correspondsto the difference between the electrostatic capacitance of the facingportion of the first electrode 41 and second electrode 31 and that ofthe facing portion of the first electrode 41 and second electrode 32,and reflects the position of the moving body 40.

A circuit that detects the electrostatic capacitance may comprise, e.g.,a capacitor bridge, as shown in FIG. 5, in which two referencecapacitors Cref are arranged in addition to a capacitor C1 formed by thefacing portion of the first electrode 41 and second electrode 31 and acapacitor C2 formed by the facing portion of the first electrode 41 andsecond electrode 32. The output signals from the second electrodes 31and 32 in response to application of the capacitance-detection voltagesignal to the first electrode 41 correspond to the electrostaticcapacitances of the capacitors C1 and C2, respectively. In place ofusing the capacitor bridge, a switched capacitor circuit, or a method ofsuperposing an RF frequency on the waveform applied to the firstelectrode 41, which is used in driving, may be employed.

According to this embodiment, the oscillation substrate 30 has twosecond electrodes, i.e., the second electrode 31 and second electrode32. As the moving body 40 moves, of the electrostatic capacitance of thefacing portion of the first electrode 41 and second electrode 31 andthat of the facing portion of the first electrode 41 and secondelectrode 32, one increases and the other decreases. The change amountsof the two electrostatic capacitances are equal. Thus, the sensitivityof the inertial driving actuator of 5 this embodiment is twice that ofan inertial driving actuator in which the oscillation substrate 30 hasonly one second electrode. From an opposite point of view, this meansthat the inertial driving actuator of this embodiment has a two-foldresolution. Thus, the position of the moving body 40 is detected with ahigher accuracy.

In the inertial driving actuator of this embodiment, if the resolutionof position detection is suppressed to almost the same degree as that ofthe actuator in which the oscillation substrate 30 has only one secondelectrode, the width (a dimension along a straight line perpendicular tothe moving direction of the moving body 40) of each of the secondelectrodes 31 and 32 can be halved. This can decrease the diameter of(can downsize) the inertial driving actuator.

[First Modification]

FIG. 6 shows the arrangement of an inertial driving actuator accordingto the first modification of the second embodiment. In FIG. 6, themembers denoted by the same reference numerals as in FIG. 3 are similarmembers. This modification employs no signal generation circuit 82, anda frictional force controller 70 also serves as the signal generationcircuit 82. Namely, in the step of detecting the position of the movingbody 40, the frictional force controller 70 generates a signal forposition detection and applies it to the first electrode 41. Accordingto this modification, the signal generation circuit 82 is unnecessary,achieving a simple arrangement. In this modification, it can be saidthat the frictional force controller 70 also serves as part of aposition detector.

[Second Modification]

In FIG. 4, the voltages applied to the second electrodes 31 and 32 areconstant voltages, and their polarities do not change. This leads to apossibility of undesirable charging of the insulating film 35 formed onthe second electrodes 31 and 32. Charging of the insulating film 35decreases the electrostatic chucking force acting between theoscillation substrate 30 and moving body 40. Then, a frictional forcesufficient to move the moving body 40 together with the oscillationsubstrate 30 may not be generated between the oscillation substrate 30and moving body 40.

FIG. 7 is a timing chart of driving and detection in an inertial drivingactuator according to the second modification of the second embodiment.In this modification, as shown in FIG. 7, in each step of moving themoving body 40, the frictional force controller 70 reverses the polarityof the voltage applied to each of the second electrode 31 and 32, andthe polarity of a rectangular-waveform voltage applied to the firstelectrode 41. This voltage application prevents charging of theinsulating film 35. Consequently, driving of the inertial drivingactuator becomes more stable. Namely, the moving body 40 is moved withthe stabler unit of predetermined distance.

[Third Modification]

FIG. 8 shows the arrangement of an inertial driving actuator accordingto the third modification of the second embodiment. In FIG. 8, themembers denoted by the same reference numerals as in FIG. 3 are similarmembers. In this modification, as shown in FIG. 8, a moving body 40A ismade of a conductive magnetic material. The moving body 40A itselfserves as the first electrode 41 identical to that described so far.

In this modification, the moving body 40A has a simple arrangement andcan be downsized easily.

[Fourth Modification]

FIG. 9 shows the arrangement of an inertial driving actuator accordingto the fourth modification of the second embodiment. In FIG. 9, themembers denoted by the same reference numerals as in FIG. 3 are similarmembers. In this modification, as shown in FIG. 9, the oscillationsubstrate 30 has second electrodes 31A and 32A. As a whole, the secondelectrodes 31A and 32A extend along a straight line parallel to themoving direction of the oscillation substrate 30. The second electrodes31A and 32A are located adjacent to each other at a gap, and this gapextends obliquely with respect to the moving direction of theoscillation substrate 30. The dimension of the second electrode 31Adecreases continuously along the straight line perpendicular to themoving direction of the moving body 40 from the left to the right of theoscillation substrate 30. On the contrary, the dimension of the secondelectrode 32A increases continuously along the straight lineperpendicular to the moving direction of the moving body 40 from theleft to the right of the oscillation substrate 30. Hence, as the movingbody 40 moves, the facing portion of the first electrode 41 and secondelectrode 31A and that of the first electrode 41 and second electrode32A change respectively in dimensions along the straight lineperpendicular to the moving direction of the moving body 40.

In this modification, the first electrode 41 always faces both thesecond electrode 31A and second electrode 32A regardless of thedimension of the moving body 40 along the straight line parallel to themoving direction of the moving body 40. Namely, the moving body 40 hasno limitations in dimension along the straight line parallel to itsmoving direction. Hence, when decreasing the moving body 40 in thisdimension, the moving body 40 is downsized and reduced in weight.

So far the embodiments of the present invention have been described withreference to the accompanying drawing. Note that the present inventionis not limited to these embodiments, but various modifications andchanges may be made without departing from the spirit or scope of theinvention.

Additional advantages and modifications will readily occur to thoseskilled in the art. Thus, the invention in its broader aspects is notlimited to the specific details and representative embodiments shown anddescribed herein, Accordingly, various modifications may be made withoutdeparting from the spirit or scope of the general inventive concept asdefined by the appended claims and their equivalents.

1. An inertial driving actuator comprising: a fixing member; a movingelement that is fixed to the fixing member and generates a smalldisplacement by extension and contraction; an oscillation substrate thatis fixed to the moving element and is moved linearly and reciprocally bythe small displacement; a moving body that is arranged on theoscillation substrate and is moved by inertia with respect to theoscillation substrate upon reciprocal movement of the oscillationsubstrate; a first electrode formed on a surface of the moving body thatfaces the oscillation substrate; a second electrode formed on a surfaceof the oscillation substrate that faces the first electrode, an area ofa facing portion of the second electrode and the first electrodechanging continuously as the moving body moves; an insulating filmpresent between the first electrode and the second electrode; africtional force controller that applies a voltage between the firstelectrode and the second electrode to exert an electrostatic forcebetween them to control a frictional force generated between theoscillation substrate and the moving body, the frictional forcecontroller changing the voltage in response to directions of thereciprocal movement of the oscillation substrate to control a relativemovement of the moving body with respect to the oscillation substrate;and a position detector that detects a position of the moving body withrespect to the oscillation substrate on the basis of an electrostaticcapacitance of the facing portion of the first electrode and the secondelectrode; wherein a width of the second electrode along a straight lineperpendicular to the moving direction of the moving body issubstantially equal to that of the first electrode.
 2. An inertialdriving actuator comprising: a fixing member; a moving element that isfixed to the fixing member and generates a small displacement byextension and contraction; an oscillation substrate that is fixed to themoving element and is moved linearly and reciprocally by the smalldisplacement; a moving body that is arranged on the oscillationsubstrate and is moved by inertia with respect to the oscillationsubstrate upon reciprocal movement of the oscillation substrate; a firstelectrode formed on a surface of the moving body that faces theoscillation substrate; a second electrode formed on a surface of theoscillation substrate that faces the first electrode, an area of afacing portion of the second electrode and the first electrode changingcontinuously as the moving body moves; an insulating film presentbetween the first electrode and the second electrode; a frictional forcecontroller that applies a voltage between the first electrode and thesecond electrode to exert an electrostatic force between them to controla frictional force generated between the oscillation substrate and themoving body, the frictional force controller changing the voltage inresponse to directions of the reciprocal movement of the oscillationsubstrate to control a relative movement of the moving body with respectto the oscillation substrate; and a position detector that detects aposition of the moving body with respect to the oscillation substrate onthe basis of an electrostatic capacitance of the facing portion of thefirst electrode and the second electrode; wherein the moving body hasmagnetism and the fixing member is provided with a permanent magnet on aside opposite to a surface on which the oscillation substrate isarranged.
 3. An inertial driving actuator comprising: a fixing member; amoving element that is fixed to the fixing member and generates a smalldisplacement by extension and contraction; an oscillation substrate thatis fixed to the moving element and is moved linearly and reciprocally bythe small displacement; a moving body that is arranged on theoscillation substrate and is moved by inertia with respect to theoscillation substrate upon reciprocal movement of the oscillationsubstrate; a first electrode formed on a surface of the moving body thatfaces the oscillation substrate; a second electrode formed on a surfaceof the oscillation substrate that faces the first electrode, an area ofa facing portion of the second electrode and the first electrodechanging continuously as the moving body moves; an insulating filmpresent between the first electrode and the second electrode; africtional force controller that applies a voltage between the firstelectrode and the second electrode to exert an electrostatic forcebetween them to control a frictional force generated between theoscillation substrate and the moving body, the frictional forcecontroller changing the voltage in response to directions of thereciprocal movement of the oscillation substrate to control a relativemovement of the moving body with respect to the oscillation substrate;and a position detector that detects a position of the moving body withrespect to the oscillation substrate on the basis of an electrostaticcapacitance of the facing portion of the first electrode and the secondelectrode; wherein the frictional force controller stops application ofthe voltage between the first electrode and the second electrode whilethe position detector detects the position of the moving body and themoving body has magnetism and the fixing member is provided with apermanent magnet on a side opposite to a surface on which theoscillation substrate is arranged.
 4. An inertial driving actuatorcomprising: a fixing member; an oscillation substrate; moving means forlinearly and reciprocally moving the oscillation substrate with respectto the fixed member; a moving body that is arranged on the oscillationsubstrate and moved by inertia with respect to the oscillation substrateupon reciprocal movement of the oscillation substrate; a first electrodeformed on a surface of the moving body that faces the oscillationsubstrate; a second electrode formed on a surface of the oscillationsubstrate that faces the first electrode, an area of a facing portion ofthe second electrode and the first electrode changing continuously asthe moving body moves; an insulating film present between the firstelectrode and the second electrode; frictional force control means forcontrolling a frictional force generated between the oscillationsubstrate and the moving body by applying a voltage between the firstelectrode and the second electrode to exert an electrostatic forcebetween them, the frictional force control means changing the voltage inresponse to directions of the reciprocal movement of the oscillationssubstrate to control a relative movement of the moving body with respectto the oscillation substrate; and position detection means for detectinga position of the moving body with respect to the oscillation substrateon the basis of an electrostatic capacitance of the facing portion ofthe first electrode and the second electrode; wherein a width of thesecond electrode along a straight line perpendicular to the movingdirection of the moving body is substantially equal to that of the firstelectrode.
 5. An inertial driving actuator comprising: a fixing member;an oscillation substrate; moving means for linearly and reciprocallymoving the oscillation substrate with respect to the fixed member; amoving body that is arranged on the oscillation substrate and moved byinertia with respect to the oscillation substrate upon reciprocalmovement of the oscillation substrate; a first electrode formed on asurface of the moving body that faces the oscillation substrate; asecond electrode formed on a surface of the oscillation substrate thatfaces the first electrode, an area of a facing portion of the secondelectrode and the first electrode changing continuously as the movingbody moves; an insulating film present between the first electrode andthe second electrode; frictional force control means for controlling africtional force generated between the oscillation substrate and themoving body by applying a voltage between the first electrode and thesecond electrode to exert an electrostatic force between them, thefrictional force control means changing the voltage in response todirections of the reciprocal movement of the oscillations substrate tocontrol a relative movement of the moving body with respect to theoscillation substrate; and position detection means for detecting aposition of the moving body with respect to the oscillation substrate onthe basis of an electrostatic capacitance of the facing portion of thefirst electrode and the second electrode; wherein the moving body hasmagnetism and the fixing member is provided with a permanent magnet on aside opposite to a surface on which the oscillation substrate isarranged.
 6. An inertial driving actuator comprising: a fixing member;an oscillation substrate; moving means for linearly and reciprocallymoving the oscillation substrate with respect to the fixed member; amoving body that is arranged on the oscillation substrate and moved byinertia with respect to the oscillation substrate upon reciprocalmovement of the oscillation substrate; a first electrode formed on asurface of the moving body that faces the oscillation substrate; asecond electrode formed on a surface of the oscillation substrate thatfaces the first electrode, an area of a facing portion of the secondelectrode and the first electrode changing continuously as the movingbody moves; an insulating film present between the first electrode andthe second electrode; frictional force control means for controlling africtional force generated between the oscillation substrate and themoving body by applying a voltage between the first electrode and thesecond electrode to exert an electrostatic force between them, thefrictional force control means changing the voltage in response todirections of the reciprocal movement of the oscillations substrate tocontrol a relative movement of the moving body with respect to theoscillation substrate; and position detection means for detecting aposition of the moving body with respect to the oscillation substrate onthe basis of an electrostatic capacitance of the facing portion of thefirst electrode and the second electrode; wherein the frictional forcecontrol means stops application of the voltage between the firstelectrode and the second electrode while the position detection meansdetects the position of the moving body and the moving body hasmagnetism and the fixing member is provided with a permanent magnet on aside opposite to a surface on which the oscillation substrate isarranged.